SSBN-726 class FBM submarines can carry 24 ballistic missiles with MIRV warheads that can be accurately delivered to selected targets from almost anywhere in the world's oceans. Earlier FBM ships carry 16 missiles. A cylindrical pressure hull structure of HY-80 steel is supported by circular frames and enclosed by hemispherical heads at both ends. The pressure hull provides an enclosure large enough for weapons, crew, and equipment with enough strength to enable the ship to operate deep enough to avoid easy detection.
A streamlined (fish-shaped) outer hull permits the ship to move quietly through the water at high speeds. This outer hull surrounds the forward and aft end of the pressure hull and is not built to withstand deep submergence pressure. It is normally considered as the main ballast tanks. The superstructure is any part of the ship that is above the pressure hull. This would include the sail or fairwater area, and the area above the missile tubes. The streamlined hull was designed specifically for efficient cruising underwater; the Skipjack was the first nuclear-powered ship to adopt this hull form.
The larger hulls accommodate more weapons of larger size and greater range, as well as sophisticated computerized electronic equipment for improved weapon guidance and sonar performance. Improved silencing techniques reduce the chances of detection.
The Ohio-class submarines are specifically designed for extended deterrent patrols. To increase the time in port for crew turnover and replenishment, three large logistics hatches are fitted to provide large diameter resupply and repair openings. These hatches allow sailors to rapidly transfer supply pallets, equipment replacement modules and machinery components, significantly reducing the time required for replenishment and maintenance. The class design and modern main concepts allow the submarines to operate for 15+ years between overhauls. Each SSBN is at sea at least 66 percent of the time, including major overhaul periods of twelve months every nine years. One SSBN combat employment cycle includes a 70-day patrol and 25-day period of transfer of the submarine to the other crew, between-deployment maintenance, and reloading of munitions.
Like all submarines in use by the U.S. Navy today, the Ohio class submarine is powered by a pressurized water reactor (PWR) driving steam turbines to a single propeller shaft. It can attain depths in excess of 800 feet at speeds in excess of 25 knots.
US strategic nuclear force structure will be adjusted to 14 Trident submarines -- four fewer than previously planned -- carrying 24 D-5 missiles, each with five warheads, per submarine. This will require backfitting four Trident SSBNs, currently carrying the Trident I (C- 4) missile, with the more modern and capable D-5 missile system. Under current plans, following START II's entry into force, the other four SSBNs will either be converted into special-purpose submarines or be retired.
